Pumping devices for supplying material to various types of machines are well known to those skilled in the art. However, to the best of applicant's knowledge, no such device is available which provides fluid at a substantially constant flow rate, provides reliable, long-term operation when used with abrasive or corrosive or viscous fluids, and minimizes the risk of leakage, ignition, or explosion of the pumped fluid or its vapors.
One prior art device was described in July of 1989, in U.S. Pat. No. 4,844,706 of Kazuo Katsuyama et al. In discussing the problems with the use of prior art rotary pumps in systems where a constant flow rate was desired, Katsuyama disclosed (at column 1) that ". . . even if the rotary pump is driven at constant number of rotation, the flow rate of the coating material may vary due to the change in the pressure loss at the suction port or discharge port of the rotary pump depending upon the flowing state of the coating material . . . and there has been a problem, e.g., in a two-component coating material that the main agent and the curing agent therefore cannot be supplied at an accurate mixing ratio."
According to Katsuyama et al., in addition to the uneven flow rate often caused by the use of a rotary pump, the use of such pump with viscous or abrasive fluids often caused a problem. Thus, at column 2 of the patent, he stated that the ". . . use of a gear pump may be considered for supplying a highly viscous paint under pressure. However, there has been a problem that the viscous coating material adheres and clogs at the bearing portion of the gear pump during long time operation to often interrupt the rotation of the pump. In addition, in the case of using a highly viscous paint, particularly a metallic paint, the metal ingredient is ground by the gear pump failing to obtain uniform coating quality."
The pumping system described in the Katsuyama et al. patent designed to solve these problems was complicated and expensive and contained at least two double-acting reciprocal pumping means, two rotary pumps, a plurality of on-off valves, timer means, a pressure control valve, and other mechanisms. However, it does not appear that the device of the Katsuyama et al. patent adequately solves either of the problems it discusses.
In the first place, it does not appear that the device of the Katsuyama et al. patent provides a substantially constant flow rate for the fluid being delivered over its entire cycle. As is disclosed at column 10 of the Katsuyama et al. patent, and illustrated in FIG. 2, the device of this patent contains two "hydraulically powered reciprocal pumps 3A and 3B;" fluid is delivered from one of such pumps until the material in such pump is substantially depleted (see from points T4 to T6 on FIG. 2), then the second of such pumps is turned on (see point T5 on FIG. 2) and fluid is delivered from it while fluid continues to be delivered from the first pump, and thereafter the first pump is turned off (see point T6 of FIG. 2) and then refilled with fluid (see from points T7 to T8 of FIG. 2); after the fluid in the second pump is substantially depleted, the cycle is repeated. At the point in the cycle where one of the pumps is turned off (see, e.g., points T6 or T10 of FIG. 2), the hydraulic fluid being furnished to side 10 of the other pump (see FIG. 1) and the coating fluid being discharged from side 9 of the other pump must accelerate sharply in their respective fluid lines, thereby substantially changing the flow rate of such fluids. In the second place, it does not appear that the device of the Katsuyama et al. patent provides reliable, long-term operation when used with abrasive or viscous fluids; for the pumping device disclosed in the Katsuyama et al. patent contacts the fluid to be delivered with the working parts of at least one rotary pump (see column 5 of the patent). Furthermore, as indicated below in the discussion of the Prus et al. patent, the fact that the Katsuyama et al. device contacts the fluid to be delivered with the working parts of at least one rotary pump often changes the rheological properties of such fluid and/or creates an explosion or pollution hazard. The Prus et al. patent also recognized certain problems with prior art pumping systems. Prus et al. disclosed a coating product installation. The Prus et al. patent stated that, when prior art gear pumps were used for the delivery of paint or varnish, they were ". . . unreliable, requiring frequent adjustment of the pump flow-rate . . . the component parts of the gear pump used under such conditions wear more rapidly. . . and . . . this wear results in internal leakage . . . . In fact, such leakage exists even when the pump is brand new. . . (see from line 67 of column 1 to line 10 of column 2)." The solution provided by Prus et al. was to connect the gear pump used in his system to a means for delivering rinsing product and to periodically flush his pump. However, in addition to causing his pump to be out of the production cycle for substantial periods of time, the use of "rinsing product" with different rheological and chemical properties tended to damage the gears in the pump and the flow rate sensors used in the system. Prus et al. recognized that ". . . abrupt changes in operating conditions resulting from the succession of products of different kinds and of very different viscosities in the conduit . . ." may cause ". . . wear of and damage to the flowrate sensor" (see Column 4, lines 19-29). However, the pumping device disclosed in the Prus et al. patent contacts the fluid to be delivered with the working parts of at least one rotary pump (see, for example, column 3). It is well known that such contact is often undesirable. Thus, for example, the turbulence and mixing caused by rotary pumps may often change the theological properties of shear-sensitive materials, such as latex (see, e.g., page 3.55 of Igor J. Karassik et al.'s Pump Handbook, Second Edition, McGraw-Hill Book Company, New York, 1984). Thus, for example, some fluids and/or their vapors (such as organic peroxides) tend to explode when subjected to shock and/or vibration and thus should not be contacted with the moving parts or seals of a rotary pump. Thus, for example, some fluids may leak from the rotary pumps that they are in contact with, thereby creating pollution and/or explosion hazards.
There are other problems with the prior art pumping systems which are not mentioned by the Katsuyama et al. and the Prus et al. patents. Thus, for example, the pumping device of the Katsuyama et al. patent is comprised of several electrical control devices which appear to be capable of generating electrical discharges. It is known that certain pumpable fluids, such as hydrocarbon solvents, are readily ignited when subjected electrical spark discharges, which are often present in electrical motors, solenoid valves, and actuators. Thus, the device of the Katsuyama et al. patent might present a fire and/or explosion hazard when used with these ignitable and/or explosive fluids.
The systems described in the Katsuyama et al. and the Prus et al. patents utilize rotary pumps, with all of the disadvantages attendant thereto. However, other pumps also present problems when an attempt is made to use them for an application requiring a constant flow rate.
Thus, by way of illustration, U.S. Pat. No. 3,937,400 of Krause describes an apparatus for spraying paint. Krause discloses that, in such an apparatus, "The use of conventional diaphragm pumps is unsatisfactory because of the pulsating nature of the feed (see lines 27-29 of column 1)." A similar teaching is presented at pages 7-24 of James P. Poynton's "Metering Pumps" (Marcel Dekker, Inc. New York, 1983); and also at pages 8-36 of Horst Fritsch's "Metering Pumps Principles, Designs, Applications" (Verlag Moderne Industrie AG& Co., Lasdsberg, Germany 1989). Recent developments in reciprocating pumps have included countermeasures to minimize the pulsation of fluid flow through the use of multiple cams which drive their respective reciprocating elements in a manner in which individual pulsations are produced such that net sum of the pulsing flows is nearly constant. Three recent disclosures of this nature are U.S. Pat. Nos. 4,556,371 of Post; 4,687,426 of Yoshimura; and 4,790,732 of Yamatani. Each of these devices fails to achieve a constant pumping flow of liquid due to the fact that the combination of cams and cam followers disclosed in each of them inherently create pulsing fluid flows which do not sum to a constant flow rate. In addition, the reliability of these pumps would be unsatisfactory when pumping fluid of an abrasive or corrosive nature: each of them places the fluid to be pumped in direct contact with components of the pump which are fabricated according to high precision manufacturing tolerances, and thus are susceptible to damage by an abrasive, corrosive, or otherwise unsatisfactory fluid. Furthermore, each of these pumps uses a complex camshaft consisting of multiple cam lobes; this type of camshaft has a high manufacturing cost, and these cam lobes must be precisely positioned relative to each other to maintain a constant flowrate of fluid.
It is an object of this invention to provide a pumping apparatus which can continuously deliver fluid without contacting such fluid with the internal part or seals of a rotary pump. It is another object of this invention to provide a pumping apparatus which can continuously deliver fluid without passing such fluid in contact with or near any devices which could generate electrical discharges.
It is an object of this invention to provide a pumping apparatus which can continuously deliver viscous and/or abrasive and/or corrosive material at a substantially constant flow rate without the need for periodic rinsing.
It is another object of this invention to provide a pumping apparatus which, during its entire cycle, does not accelerate the fluid being pumped to the degree experienced in conventional reciprocating pumps.
It is another object of this invention to provide a pumping apparatus which does not subject the fluid being pumped to any substantial amount of shear.
It is an object of this invention to provide a pumping apparatus which can continuously delivery viscous and/or abrasive and/or corrosive material at a substantially constant flow rate which is substantially more reliable than prior art pumping devices.
It is another object of this invention to provide a pumping apparatus which is relatively uncomplicated and inexpensive.
It is an additional object of this invention to provide a novel timing means consisting of a cam and cam followers, the geometry of which results in reciprocating motion which can drive fluid at a constant flow rate.
It is yet another object of this invention to provide a novel pumping apparatus comprised of reciprocating elements which is capable of delivering fluid at a constant flow rate without contacting said fluid with any of the parts of the reciprocating elements.